When using AEC, what should the radiographer set the backup time to, in relation to the total expected exposure time?

• A. 100%
• B. 125%
• C. 150%
• D. 200%

Answer: (C)

When utilizing Automatic Exposure Control (AEC), it is important for the radiographer to set the backup time to a level that ensures patient safety while still allowing for adequate exposure time under normal circumstances. Setting the backup time to 150% of the total expected exposure time is a common practice. This means that if the AEC system fails to reach the prescribed exposure within the set time, the backup system will terminate after 150% of the anticipated exposure duration.

This approach balances the need to minimize unnecessary radiation exposure to the patient with the need to guarantee that the image will be adequately exposed. A setting of 150% provides a sufficient buffer to account for variations in patient thickness, positioning, or other factors that might affect exposure without risking excessive exposure time, which could be harmful.

The rationale behind not choosing lower percentages, such as 100% or 125%, is that they may not provide an adequate margin of safety in the case of unexpected factors causing a delay in achieving the appropriate exposure. Meanwhile, choosing overly high settings like 200% could result in excessive radiation exposure without justifiable benefit. Thus, setting the backup time to 150% ensures a safe and effective approach to radiographic imaging when employing AEC.